Pandemonium erupted at a Harlem elementary school yesterday after a teacher came into contact with a substance he feared was anthrax.

Health officials said they did not believe the powdery white substance discovered in an envelope was the potentially deadly bacteria – but took it for testing anyway.

The teacher, Vladimir Kundel, said he opened a letter containing the powder while talking to another teacher in a lounge.

“She told me, ‘Be careful with the envelope’ and, just then, the white powder popped out and scattered on top of the table and onto the bottom of my slacks,” he said.

“I left the envelope in the room, and I ran to the main office on the second floor. I had the powder on my hands.”

Kundel said the letter was addressed to another teacher and was mistakenly put in his mailbox.

He is taking the antibiotic Cipro, pending test results.

“Everybody is jittery,” said Randi Weingarten, president of the United Federation of Teachers.

“All signals suggest that this was a stupid, despicable hoax.”

None of this allayed the fears of parents who arrived at PS 194 at 244 W. 144th St. to pick up their children. Eleven students were taken to the Harlem Hospital emergency room by parents. All were released.

“I’ll keep my daughter out of school until I hear otherwise,” Keith Clark, a third-grader’s father, said.

Nervous students say they nearly panicked when the public-address system broadcast a warning.

They were taken to the school auditorium, where they were later released to their parents.

“There was an announcement over the loudspeaker: ‘Don’t drink the water, and don’t go to the bathroom,'” said fourth-grader Diamond Davis, 9.